Minecarts stop moving before entering the last loaded chunk(read: "end of the world").
To reproduce, create a long ((render distance + 1) * 16) minecart track, when riding the track from either end, the minecart will freeze up a little bit before the end of the track. The track I happened to be using traveled north/south.
The screenshot was taken while the minecart was frozen right before entering the last chunk before the end of the world
Related to MC-90163
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[media]
Dupe of MC-89915